1. Field of the Invention
The present invention generally concerns the management of power in microprocessor-controlled devices communicating across telephone lines, including in terminal devices. The present invention particularly concerns the telephone-line-recharging of the battery within a battery-powered telephone device. The present invention further particularly concerns the temporary removal of power from circuits that interface to a terminal's microprocessor during the standby operational mode of such microprocessor in a manner that prevents current drain from the charged communication lines of the microprocessor.
2. Background of the Invention
Devices that communicate across telephone lines, such as voice telephones, are commonly powered by the telephone lines. Telephone lines are energized at a central telephone switching station, or at a booster repeater, to a nominal voltage of about 48 v.d.c. Because of the resistance of its wires, the voltage across telephone lines drops with increasing spatial distance from points where the lines are charged. Over a great distance, typically many miles or kilometers, the voltage may typically drop to as little as 2-3 v.d.c.
In order for a telephone-line-connected device that contains electrical circuits requiring a fixed power supply voltage, nominally 5 v.d.c., to (i) function and (ii) communicate reliably across telephone lines when connected to such telephone lines at a point of low voltage potential, it is useful for the device to contain its own internal power source. Such an internal power source may be derived from normal a.c. wall power, or may alternatively be, especially in the case of a portable telephone device, derived from a self-contained power source, typically a battery. A self-contained internal power source such as a battery is also useful in portable telephone devices that are occasionally disconnected from the telephone lines and that need power during such periods of disconnection. Telephone devices may need power while disconnected, for example, in order to begin operation and to respond to operator commands before being connected to the telephone lines.
When a portable telephone device is powered by batteries then a problem is presented in maintaining the charged state of the batteries. If the batteries are disposable then they must be periodically tested, and must be disposed of when weak or over aged. When the batteries are rechargeable then they must be periodically recharged from an external source of power, normally from wall power. It is sometimes difficult to assess the charge condition of batteries, and to reliably maintain them in a fully charged state by regular maintenance. Accordingly, it would be desirable if a telephone device were able to use batteries while somehow reducing the maintenance requirements of such batteries.
In a related art area that also concerns the power consumption of telephone devices, it may be noted that the magnitude of the permissible, and occasionally mandated, direct current flow from telephone lines into a telephone, or telephone device, is generally large in relation to the power requirements of modern, solid state, telephone circuitry. For example, in order to produce the off-hook signal by which a central telephone exchange may recognize that a telephone, or telephone device, is connected to a telephone line, the telephone must draw, by specification, a minimum of 10 milliamperes direct current. The current drain by a telephone or telephone device is typically much greater, and may range to 100 milliamperes or more. This current is considerably larger than that which might be consumed by several solid state chips which, in aggregate, comprise a modern telephone or telephone device such as, for example, a terminal. For example, circuits including a commonly available microprocessor, a random access memory (RAM), a modem, a DTMF dialer, and a Liquid Crystal Display (LCD) might collectively be powered by a current of approximately 12 milliamperes at 5 v.d.c. It is thus the case that not only modern voice telephones, but also other digital electronics devices such as terminals, may readily be entirely powered by their connection to telephone lines--at least when such telephone lines maintain a voltage differential that is greater than the voltage requirements of the telephone device, typically 5 v.d.c.
In still another art area regarding telephones, it is known to make direct, non-transformer-coupled, connection of subscriber station telephone equipments to telephone lines. For example, one such connection is taught in U.S. Pat. Ser. No. 4,303,805 for a SUBSCRIBER STATION NETWORK to two inventors including one inventor of the present invention.
In still another art area, it is known that power may be conserved in certain microprocessor-based digital systems by declocking the microprocessor, and causing it to stop in a mode called "standby". This is particularly true of a microprocessor implemented in Complementary Metal Oxide Semiconductor (CMOS) logic that is based on Field Effect Transistors (FETs). CMOS logic uses appreciable power only when transitioning from one logical state to the other. If no clock is enabled, and no logic transitions ensue, then the power consumption of a CMOS technology microprocessor chip typically drops to the order of several microamperes at 5 v.d.c. One gate in the microprocessor, which gate is typically connected to an external switch or signal, typically remains active during the declocked state of the microprocessor. This gate remains active for receipt of an external signal such as may result from a manual switch activation. Upon the receipt of this external signal the microprocessor's clock is reenabled, and logic operations may be recommenced.
Although a CMOS technology microprocessor does not itself consume appreciable power when declocked in standby mode, the communication signal line drivers of such microprocessor may, in some cases, maintain the microprocessor's communication signal lines at a logic High, non-zero voltage, level. These signal lines connect to the receivers of other electronic circuits with which the microprocessor communicates. Normally these receivers are of high input impedance. Consequently, only a reasonable percentage of a running microprocessor's total power budget is consumed in switching its signal lines.
It may, however, be the case that upon such times as the microprocessor is declocked and placed in standby mode in order to reduce its operational power consumption that those electronic circuits to which the microprocessor connects across its communication lines are also, simultaneously, unpowered. The controlled and selective disruption of power to these circuits is conventionally accomplished by selectively disabling the supply of power voltage to these circuits. When the circuits are unpowered then the receivers in such circuits present an undesirable current leakage path to ground for the charged communication lines. This current drain must be supplied by the microprocessor. It increases the microprocessor's power consumption in its declocked, standby, mode.
Accordingly, it would be useful if a declocked, standby, microprocessor connecting through signal lines to one or more unpowered electrical circuits could have its current drain, and power loss, from its charged communication signal lines either be reduced or eliminated.